Getter pump module and system

ABSTRACT

A getter pump module includes a number of getter disks provided with axial holes, and a heating element which extends through the holes to support and heat the getter disks. The getter disks are preferably solid, porous, sintered getter disks that are provided with a titanium hub that engages the heating element. A thermally isolating shield is provided to shield the getter disks from heat sources and heat sinks within the chamber, and to aid in the rapid regeneration of the getter disks. In certain embodiments of the present invention the heat shields are fixed, and in other embodiments the heat shield is movable. An embodiment of the present invention also provides for a rotating getter element to enhance getter material utilization.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/332,564, entitled IN SITU GETTER PUMP SYSTEM AND METHOD byinventors D'Arcy H. Lorimer and Gordon P. Krueger, filed Oct. 31, 1994,now U.S. Pat. No. 5,685,963, and which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

This invention relates generally to ultra-high vacuum systems, and, moreparticularly, to in situ getter pumps used in semiconductormanufacturing systems.

There are a number of processes which require ultra-high vacuum levelsof, for example, 10⁻⁷ to 10⁻¹² Torr. For example, high vacuum physicsmachines such as cyclotrons and linear accelerators often require avacuum of the order of 10⁻⁸ -10⁻¹² Torr. Also, in the semiconductormanufacturing industry, ultra-high vacuums of approximately 10⁻⁷ -10⁻⁹Torr are often required in semiconductor processing equipment.

Several pumps are often used in series or parallel to achieve ultra-highvacuum levels within a chamber. A mechanical (e.g. oil) pump is oftenused to reduce the pressure within a chamber to approximately 30-50millitorr. These are often referred to as "high pressure" pumps sincethey only pump relatively high pressure gasses. Then, a high- orultra-high vacuum pump, such as a molecular pump, cryopump, turbo pump,or the like, is used to reduce the pressure to approximately 10⁻⁷ -10⁻⁹Torr. These are often referred to as "low pressure" pumps since theypump low pressure gasses. The pump-down time for a particular chambercan range from minutes to hours to days depending upon such factors asthe size of the chamber, the capacity of the pumps, the conductance fromthe chamber to the pumps, and the desired final pressure.

In certain ultra-high vacuum applications, getter pumps have been usedin conjunction with the aforementioned mechanical, molecular, andcryopumps. A getter pump includes getter materials comprising metals ormetal alloys which have an affinity for certain non-noble gases. Forexample, depending upon the composition and temperature of the gettermaterial, getter pumps have been designed which preferentially pumpcertain non-noble gases such as water vapor and hydrogen.

For example, getter pumps provided by SAES Getters, S.p.A. of Milan,Italy, typically include getter material encased in a stainless steelcontainer. Getter pumps can operate from ambient temperatures to about450° C., depending upon on the species of gas to be pumped, the gettercomposition, etc. A preferred getter material for prior art SAES getterpumps is St 707 getter material (which is an alloy of Zr--V--Fe) andwhich is produced by SAES Getters, S.p.A. of Milan, Italy. Another suchmaterial is St 110™ getter alloy, also available from SAES Getters,S.p.A., which is an alloy of Zr--Al. Some of these prior art getterpumps can be considered in situ pumps in that they are disposed withinthe high vacuum physics machines.

Some present getter pump designs employ getter devices comprising metalribbons coated with a powdered getter material such as the St 707 and St101™ getter alloys just described. The coated ribbons are pleated in aconcertina fashion to increase the ratio of exposed surface area to thevolume occupied by the coated ribbon, and to increase adsorption ofdesired gasses. Such pumps are manufactured by SAES Getters, S.p.A., andsold under the trade name SORB-AC®. In addition, recent designs haveemployed disk-shaped substrates coated with getter material powders.Designs using coated substrates have a drawback in that the total amountof getter material available for sorption is limited to the nominalsurface area of the getter device substrate.

It is has been suggested that getter pumps be provided for semiconductorprocessing equipment. For example, in an article entitled"Non-Evaporable Getter Pumps for Semiconductor Processing Equipment" byBriesacher, et al., and published in Ultra Clean Technology 1(1):49-57(1990), it is suggested that any application which uses getters topurify processed gases for semiconductor processing can also utilizenon-evaporable getter pumps for in situ purification and for theselective pumping of impurities.

The aforementioned Briesacher reference discloses that there are twopossible operating scenarios for the use of getter pumps in a sputteringsystem, which is a type of semiconductor processing equipment. The firstis the addition of the getter pump to the system to operate in parallelwith conventional pumps (e.g. mechanical and cryopumps) of the system.In this scenario, the operation of the system is not modified in anyway, and the getter pump merely serves as an auxiliary pump to lower thepartial gas pressure of certain components of the residual gas in thechamber. The second scenario requires filling the chamber to a pressurein the range of 3×10⁻³ to 6×10⁻³ Torr, stopping the argon flow into thechamber, and sealing the chamber. The getter pump is then said to act asan "in situ" purifier for the argon. However, as discussed below, thepump is not truly "in situ" in that the active material is not withinthe volume of the processing chamber.

In a typical sputtering system, a noble gas (usually argon) is pumpedinto a chamber and a plasma is created. The plasma acceleratespositively charged argon ions towards a negatively charged target,thereby causing material to become dislodged and to settle on thesurface of the wafer. Getter pumps are well adapted for use withsputtering systems, since the only desired processing gas is a noble gaswhich is not pumped by the getter pump. Therefore, the getter pump canremove impurity gases from a sputtering chamber without affecting theflow of the noble gas required for the sputtering process.

The Briesacher reference was primarily an academic analysis of thepracticality of using non-evaporable getter pumps in semiconductorprocessing equipment. Therefore, very little practical application ofthe theory is disclosed. Furthermore, while the Briesacher article usesthe term "in situ" to describe a scenario for the use of a getter pump,it is clear from the description that the getter pump is external to thechamber and is considered "in situ" only in the sense that when thechamber is sealed and when no argon is flowing into the chamber, thevolume within the getter pump can be considered to be connected to thechamber volume. According to the analysis presented by Briesacher, avalve must be placed between the getter containment vessel and the mainchamber to protect the getter from atmospheric exposure that woulddeteriorate the getter and require additional regenerations. Suchprotection is imperative with the strip-type getters discussed in theBriesacher reference. Thus, the getter described by Briesacher is nottruly "in situ" in that the getter pump surfaces are within a volumethat is connected to the chamber volume through a restrictive throat,which greatly limits the conductance between the chamber and the pump.By "conductance" it is meant herein the ease with which a fluid (gas inthis instance) flows from one volume (e.g. the processing chamber) toanother volume (e.g. the pump chamber). Conductance is limited by theaperture size between the two chambers, which is typically thecross-sectional area of the throat of the cryopump.

SUMMARY OF THE INVENTION

The present invention provides an improved getter pump module and systemthat is particularly well adapted for in situ pumping of semiconductorprocessing chambers.

In one preferred embodiment, the present invention includes getter pumpshaving a plurality of getter elements, the getter elements comprisingporous, sintered getter material having an aperture extendingtherethrough and a support element extending through the aperture.Titanium or other metal hubs are typically provided in the apertures ofthe getter elements to provide mechanical support for the getterelements and to enhance thermal transfer between the heating element andthe getter elements. The getter elements, which are typically diskshaped, are preferably partially surrounded by a shield which providesthermal isolation between the getter elements and other devices andsurfaces within a semiconductor processing chamber, and which also aidsin the getter element regeneration process.

In a preferred embodiment, a radiative heater is used to heat the gettermaterial. In another preferred embodiment, the present inventionincludes getter pumps in which the faces of adjacent getter elements arenot parallel, which getter elements include apertures through which aheating element is extended. In preferred embodiments, the aperturesdefine an axis and the getter elements are arranged at angles notperpendicular to the axis. In another embodiment, the apertures aresubstantially perpendicular to the axis, but the faces of adjacentgetter elements are inclined with respect to each other, preferably atequal and opposite angles.

In still another embodiment, the present invention includes asemiconductor processing system comprising a processing chamber, an insitu getter pump having a plurality of getter elements, each having anaperture extending therethrough, and a support element extending throughthe aperture. The getter pump has an actual pumping speed with respectto the processing chamber which is at least 75% of the theoreticalpumping speed of the plurality of getter elements in an unlimitedvolume.

The present invention also includes a method for processing a waferwhich includes the steps of (a) placing a wafer within a processingchamber, the chamber including an in situ getter pump having aconductance of greater than about 75% disposed within the waferprocessing chamber, the in situ getter pump including a plurality ofgetter elements; (b) sealing the chamber; (c) flowing a noble gas intothe chamber while simultaneously pumping the chamber with an externallow pressure pump and the in situ getter pump, the low pressure pumpoperative to remove noble gasses from the chamber and which in situgetter pump operative to remove non-noble gasses from the chamber; and(d) processing the wafer in the chamber while flowing the noble gas intothe chamber. The present invention also includes the wafer produced bythe method of the invention.

In yet another embodiment, the present invention includes a method forpumping a chamber, which includes the steps of (a) sealing the chamberfrom the external atmosphere; and (b) pumping the chamber with an insitu getter pump disposed within the chamber, the in situ getter pumphaving a conductance of greater than about 75% and the in situ getterpump being capable of operating at more than one temperature to pumpthereby selected non-noble gasses at different getter temperatures.

Additional aspects and advantages of the invention will become moreapparent when the following description is read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF TEE DRAWINGS

FIG. 1 is a pictorial representation of a semiconductor processingsystem, including an in situ getter pump module of the presentinvention.

FIG. 2 is a partial perspective view a number of getter elements of theinvention and a thermally isolating shield.

FIG. 3 is a facing view of a getter element of FIG. 2.

FIGS. 4A and 4B illustrate sectional views of getter elements of theinvention. FIG. 4A is a sectional view of a single getter element takenalong the line 4A--4A of FIG. 3. FIG. 4B is a sectional view of threeabutting getter elements, also along taken the line 4A--4A of FIG. 3.

FIG. 5 is an illustration of the number of collisions between a moleculeand two adjacent getter elements of the invention as a function of thedistance between the getter elements.

FIGS. 6A and 6B illustrate certain dimensional parameters of the getterelements of the invention. FIG. 6A illustrates dimensional parameters ofadjacent getter elements in a arcuate configuration. FIG. 6B illustratesdimensional parameters for adjacent parallel getter elements.

FIG. 7 is a graphical representation of the relationship between pumpingspeed and the distance "d" between adjacent getter elements.

FIG. 8 is an illustration of another embodiment of the invention whereinadjacent getter elements are arranged at opposing angles.

FIG. 9 is an illustration of yet another embodiment of the inventionwherein the facing sides of adjacent getter elements are non-parallel.

FIG. 10 illustrates an embodiment of the invention wherein an array ofgetter elements is arranged partially circumferentially around asputtering platter.

FIG. 11 is an illustration of an embodiment of the invention whereinstar-shaped arrays of getter elements are supported on a rotatingsupport element.

FIG. 12 is a side view of the embodiment shown in FIG. 11, but whereinthe getter elements are inside a thermally isolating shield.

FIG. 13 is a side view of the embodiment illustrated in FIG. 2, butwherein the getter elements are inside a thermally isolating shield.

FIGS. 14A and 14B illustrate a side view of a thermally isolating shieldof the invention which moves between open and closed configurations.FIG. 14A illustrates a closed configuration in which the getter elementsare thermally isolated. FIG. 14B is an illustration of an openconfiguration in which the getter elements are exposed to thesurrounding environment.

FIG. 15 is a partial cut-away view of the embodiments shown in FIGS. 14Aand 14B, further showing gas sources.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a portion of a semiconductor processing system 100 inaccordance with the present invention. The processing system includes awafer processing chamber 102 having an interior wall 103. An externalpump 104 ("P"), such as a cryopump and/or a mechanical pump, is coupledto the chamber by a conduit 105 to reduce the internal atmosphericpressure of the chamber before the getter pump module is operated.Preferably, the internal pressure of the chamber is brought to a levelof about 10⁻⁶ bar before the getter pump is activated. Inside chamber102 is included a sputtering stage 106 which includes a chuck 108 thatrests atop a support 110. Also included are heat lamps 112 and 112' andat least one in situ getter pump module such as shown generally at 114and 116. Chamber 102 typically is one component of a multicomponentsemiconductor processing system which includes, inter alia, variouspower sources, analyzers, cryopumps, plasma generators, low vacuumpumps, high vacuum pumps and controllers. These other components,including their design, manufacture and operation, are well known tothose of skill in the art.

As used herein, the phrase "in situ getter pump" will refer to a getterpump where the active elements, i.e. the active getter material, isphysically located within the same volume of space as the wafer beingprocessed. As such, the conductance between the in situ getter materialand the process chamber is very high compared to the coupling of anexternal getter pump to the chamber through a gate valve, conduit, thethroat of a pump, etc. This results in a relatively high pumping speed.For example, with an in situ getter pump of the present invention, morethan 75% of maximum theoretical pumping speed can be achieved, ascompared to at best 75% of maximum theoretical pumping speed for anexternal getter pump coupled to the processing chamber with a gate valveor the like.

The getter pump module 114 and/or 116 is "activated" by heating thegetter material of the getter pump to a high temperature, e.g. 450°C.This activation of the getter pump is required because the gettermaterial becomes "passivated" upon exposure to the atmosphere, and mayoverlap with a "bake-out" step wherein lamps 112 and 112' are used tobake out the chamber to rid the chamber of residual gasses, moisture,etc. However, the bake out period and the activation periods need notcoincide.

With continuing reference to FIG. 1, in situ getter pumps 114 and 116will now be described in greater detail. Pumps 114 and 116 preferablyinclude thermally isolating shields 118 and 126 respectively. Theshields may further include thermally reflective interior walls 120 and128 to enhance the regeneration of the getter elements by reflectingback heat to the getter elements. Within the thermally isolating shieldsare getter assemblies 122 and 130 which are supported on supports showngenerally at 124 and 132. Getter assembly 114 is illustrative of a "lowboy" configuration which may be required due to space limitations withinthe processing chamber. Getter module 126 is an example of a preferred"high boy" configuration which provides a relatively greater conductancebetween the getter assembly 130 and the interior of the processingchamber due to a relatively greater opening than that which is providedby the low boy configuration.

The getter pumps 114 and 116 further include heaters 134 and/or 134',and 136 and/or 136', respectively, for heating the getter material totemperatures effective to "activate" the getter material as describedabove, and/or to control the adsorption characteristics of the gettermaterial as is well known in the art. Heaters 134, 134', 136 and 136'can be resistive heaters, i.e., heaters that use at least in partelectrical resistance for heating, or radiative heaters, i.e., heatersthat employ radiation to effect heating of nearby surfaces. Preferably,heaters 134 and 136 are resistive heaters and are disposed through anaperture in the getter elements as will be described in greater detailbelow. It will be appreciated that heaters 134 and 136 can also fulfilla support function, supporting the getter elements in addition toheating the getter material. Heater elements 134' and 136' arepreferably radiant heaters and are disposed proximate to the gettermaterial and the walls of the thermally isolating shield. It will beappreciated that heater elements 134' and 136' may be disposed atvarious locations within the thermally isolating shield. Preferredlocations are those from which the heaters can efficiently heat thegetter material to the desired temperatures without affectingsignificantly structures within the processing chamber.

An in situ getter pump in accordance with the present invention isillustrated at 114 in FIG. 2. The pump includes a getter assembly 122and an elongated, box-shaped thermally isolating shield 118 forthermally isolating the getter assembly from the interior of thesemiconductor processing chamber 102. Although the shield 118 ispreferred, it can be eliminated if the getter assemblies are positionedor otherwise shielded from the heated surfaces in the chamber.

Getter assembly 202 includes a plurality of disk-shaped getter elements204, each comprised of getter material 206. The getter elementspreferably include a centrally located aperture 208, through whichaperture extends a support element 210 to physically support theelements. In a preferred embodiment, the aperture is a substantiallycylindrical bore extending through the getter element. Other apertureconfigurations will be recognized to be equivalent. Support element 210can farther include a resistive element 212 running through the supportelement to form a resistive heating element to heat to the getterelements to a regeneration temperature in addition to lower temperaturesat which the getter material will remove certain gasses preferentiallyfrom the atmosphere as is well known in the art. The support elementpreferably is of a tubular, cylindrical design formed from stainlesssteel, and is dimensioned to engage with the aperture to providecontact, including thermal contact, with the getter elements. Supportelements are available commercially from various suppliers. Supportelements which are effective to act as heating elements are soldcommercially by Watlow.

In a preferred embodiment, the heating of the getter material isperformed using heater element 134' located proximate to the gettermaterial. Heating element 134' is preferably a radiative heater, e.g., aSylvania quartz infrared lamp such as available commercially fromOsram-Sylvania of Winchester, Ky., USA. Preferably, the heating element134' runs in a direction substantially parallel to the path defined bythe axes of the getter elements, which can be supported by a simple(i.e., unheated) rod, preferably of stainless steel. It will beappreciated that a metal supporting rod can also provide heat to thegetter material by conduction. Other arrangements of the heater andgetter elements will be apparent to those of skill in the art. Forexample, the getter elements may be held in other fashions, such as bytheir edges. The heating element can be a single integral heatingelement, as shown in FIG. 2, or it can comprise a series of discreteheating elements.

The thermally isolating shield 118 comprises an exterior surface 216which is effective to block radiant heat from the external heat sourceswithin the chamber from affecting the getter elements. The shield mayalso include a thermally reflective interior surface 120 facing thegetter elements which functions to increase regeneration efficiency byreflecting heat back onto the getter assemblies during theirregeneration. In addition, the interior surface of the shield can alsoserve to prevent heat from the regeneration of the getter elements fromreaching surfaces within the chamber outside of the thermally isolatingshield 118. In a preferred embodiment, the shields are made from 316Stainless Steel which as been electropolished to about 25 RA.

A preferred embodiment of a single getter element is shown in FIG. 3 at204. This preferred getter element comprises a solid, porous, sintereddisk of getter material 206 which disk includes a non-getter metallichub 304 disposed within the aperture of the disk and a non-gettermetallic spacer 306. The spacer and hub define an aperture 208 which ispreferably cylindrical and dimensioned to receivably engage thesupport/heating element. In preferred embodiments, both the hub andspacer are made from titanium. As used herein, the term "disk" refers toa getter element having a substantially circular or ovoid outerperiphery and a surface area in excess of its thickness. Although asubstantially planar getter element is preferred for reasons which willbecome apparent below, deviation from planarity is also encompassed bythe present invention.

By "solid" it is meant that the getter material comprises the body ofthe getter element, such as described in U.S. Pat. No. 5,320,496 toManini, et al., entitled "High-Capacity Getter Pump", and which isincorporated herein by reference, as opposed to other getter elementswherein getter material is adhered to a substrate surface. By providinga solid, porous getter disk, pumping efficiency and impurity capacity isgreatly increased since molecules can be adsorbed deep into the body ofthe getter element, rather just on the surface as with prior art getterelements.

The getter elements can be made from a variety of getter materials,depending upon their desired properties. Typical getter materialsinclude alloys of zirconium, vanadium and iron as disclosed in U.S. Pat.Nos. 3,203,901, 3,820,919, 3,926,832, 4,071,335; 4,269,624, 4,428,856,4,306,887, 4,312,669, 4,405,487, 4,907,948 and 5,242,559; and BritishPatent No. 1,329,628 and British Patent Application No. GB 2,077,487A;and German Patent No. 2,204,714, each of which is incorporated herein byreference. Additional types of getter materials include, among others,titanium, hafnium, uranium, thorium, tungsten, tantalum, niobium, carbonand alloys thereof.

A preferred getter material comprises a zirconium--vanadium--ironternary alloy having a weight composition such that the percentages ofweights of the three metals, when plotted on a ternary compositiondiagram fall within a triangle whose vertices lie at a) 75% Zr/20% V/5%Fe; b) 45% Zr/20% V/35% Fe; and c) 45% Zr/50% V/5% Fe. More preferably,the getter material comprises a ternary alloy having a composition of70% Zr/24.6% V/5.4% Fe by weight, which ternary alloy is sold under asSt 707 by SAES GETTERS, S.p.A. Such materials are described in U.S. Pat.No. 4,312,669 and British Patent Application No. GB 2,077,487A.

Another preferred getter alloy is one made from zirconium and aluminum,comprising about 84% zirconium by weight and 16% aluminum by weight.Such material is sold under the trade name St 101® by SAES GETTERSS.p.A. Still another preferred getter material comprises 17% carbon and83% zirconium by weight and is sold under the trade name St 171® by SAESGETTERS S.p.A. Yet another preferred getter material comprises 82%zirconium, 14.8% vanadium and 3.2% iron by weight and is sold under thetradename St 172 by SAES GETTERS S.p.A. Another preferred gettermaterial comprises 10% molybdenum, 80% titanium and 10% titanium hydride(TiH₂) by weight and is sold under the tradename St 175 by SAES GETTERSS.p.A. Those of skill in the art will appreciate that these gettermaterials can be prepared by analogy to the descriptions in theabove-cited patents and patent applications.

Highly porous getter materials tend to be preferable to less porousmaterials in that they tend to have higher adsorption capabilities. Suchporous getter materials can be prepared in accordance with thedescriptions in U.S. Pat. No. 4,428,856, which describes the preparationof porous getter bodies from a mixture of powders including titanium,titanium hydride and a refractory metal chosen from the group consistingof tungsten, molybdenum, niobium and tantalum; British PatentApplication No. GB 2,077,487A, which describes the preparation of porousgetter material from a mixture of zirconium and the above-describedternary alloy; and German Patent No. 2,204,714 which describes thepreparation of a porous getter material comprising a mixture ofzirconium and graphite powders.

Preferred getter materials and their preparation are described inBritish Patent Application No. GB 2,077,487A. The preferred gettermaterials comprise mixtures of zirconium powder with the above-describedternary alloy in a ratio of between 4 parts zirconium to 1 part ternaryalloy and 1 part zirconium to 6 parts ternary alloy by weight. Morepreferably, the zirconium:ternary alloy ratio is between 2:1 and 1:2.The ternary alloy can be formed, for example, by combing zirconiumsponge with commercially available iron-vanadium alloy (Murex, UnitedKingdom) in a fusion furnace under reduced pressure until molten,cooling the molten material, and milling the resulting solid to apowder.

Formation of the getter elements can be accomplished using a processwhich comprises placing a hub (described below) into a getter elementmold, adding the alloy and the zirconium powders and sintering thematerial at a temperature between about 1000° C. and 1,100° C. for aperiod of between about 5 minutes and about 10 minutes.

FIG. 4A shows a cross section of the getter element shown in FIG. 3taken along the line 4A--4A at 204. As shown in FIG. 4A, the getterelement includes a porous sintered disk of getter material 206 whichdisk includes a hub 304 of non-getter material disposed in an aperturewithin the disk. The hub includes a foot 406 and a central aperture 208.Preferably, the foot of the hub is substantially flush with the disksurface while the opposite end of the hub extends above the surface ofthe disk. However, it will be appreciated that either or both ends ofthe hub may extend above the disk.

The diameter of a preferred getter element of the present invention isabout 25.4 millimeters (mm). The thickness of the getter disk is about1.3 mm. A preferred hub embodiment includes a substantially circularfoot having a diameter of about 8.0 mm, and a foot height of about 0.3mm; and a substantially circular raised portion extending from the foot,the raised portion having a diameter of about 6.0 mm and a height ofabout 1.7 mm (i.e., the total height of the hub is about 2.0 mm). Thus,in is preferred embodiment the raised portion extends above the gettermaterial at a height of about 0.7 mm from the disk surface. The diameterof the aperture extending through the hub that receives the heatingelement or support is about 3.8 mm.

In preferred embodiments, getter pumps are constructed from a pluralityof getter disks which are placed adjacent each other along the axesdefined by the disks' apertures. Such an embodiment is illustrated inFIG. 4B at 450. As shown in FIG. 4B, the getter elements includes afirst disk 206a, a second disk 206b, and a third disk 206c. Each disk isaligned such that a central aperture 208' is formed by the apertures ofthe individual disks. In order to maximize the available surface area,it is preferable to stack the disks such that the hub of any one disk issubstantially touching the spacer of an adjacent disk. Thus, hub 304a ofdisk 206a is shown in contact with spacer 306b of disk 206b, and hub304b of disk 206b is in contact with spacer 306c of disk 206c. It willbe appreciated that the spacers provide gaps through which the gettermaterials can interact with the atmosphere to which the getter pump isexposed. Such gaps are illustrated at 472 and 472', which are formed byopposing faces 476 and 478; and gaps 474 and 474', which are formed byopposing faces 480 and 482. As shown in the Figure, faces 484 and 486 ofthe getter elements at the ends of the stack are free. Typically,however, there will be many getter elements stacked to provide many ofsuch gaps.

Referring to FIG. 5, the parameters required for optimal pumpingfunction will be discussed. As it is well known in the art, theefficiency of a getter pump is related to the distance between thegetter elements. If the getter elements are spaced too widely, gasmolecules will pass between the walls after a few, or no collisions withthe getter material. This is illustrated at 500 where adjacent getterelements 204b and 204a are spaced at a distance which allows molecule506 to collide with either opposing face of the getter elements only afew times along path 508 before passing between the disks without beingadsorbed. Conversely, as the getter elements are brought together, morecollisions between the molecule and the getter element surfaces occur,thereby increasing the likelihood that the molecule will be trapped bythe getter material. This is illustrated at 510 where opposing getterelements 204d and 204c are spaced close enough that molecule 516collides several times along the opposing getter element faces alongpath 518. Each time the molecule collides with a getter element surface,there is a certain probability that the molecule will stick to thesurface and become absorbed therein. Thus, a greater number ofcollisions between the molecule and the surface will yield acorrespondingly greater likelihood that the molecule will be trapped bythe surface. However, if the getter elements are placed too closetogether (e.g., if they abut each other), the edge area of the disk willbecome the dominant pumping surface, which is less effective than thefacing surfaces of the disks.

In view of the foregoing, preferred getter element designs will takeadvantage of the above-described properties to optimize the efficiencyof the getter pump by employing various geometries, see, e.g., WO94/02957, published Feb. 3, 1994, to Ferrario, et al., and TechnicalPaper TP 202, American Vacuum Society 39th National Symposium (1992),both of which are incorporated herein by reference. The relevantparameters to be considered are shown in FIG. 6A by reference toopposing disks 206b and 206a. The relevant parameters include the diskradius "D," inter-element spacing "d" and disk thickness "t." In someembodiments, the getter elements will be arranged in a fan pattern suchas that shown at 610 in FIG. 6B. There, disks 206e, 206d, and 206c arearranged in an arcuate pattern having an angle "α" between the disks.Thus, the inter-element spacing d will be related to the angle α and thelength l of the getter element.

The above-described relationship between the arrangement and dimensionsof the getter elements and the efficiency of the getter pump isillustrated in FIG. 7 along path 700, which shows the relationshipbetween pumping speed "S" and the inter-element distance "d" asdetermined by experimental tests of disk performance as a function ofthe above-described parameters. As seen in FIG. 7, when the getterelements are touching, i.e., when d=0, the pumping speed is at the value"S₁." As the inter-element spacing increases, the pumping speedincreases until reaching a maximum at which point further increases inthe distance between getter elements allow fewer molecular reflectionsbetween the disks; thereby increasing the probability that the moleculewill fly between the surfaces of the disks. By extending the distancebetween adjacent getter elements sufficiently, the pumping speed can bedecreased below that for the case where all of the getter elements aretouching. The optimum parameters for disk spacing can be determined byplotting the pumping speed versus the disk spacing and finding themaximum of the resulting distribution. For the aforementioned 25.0 mmdiameter disk shaped getter elements, a spacing of about 0.7 mm ispreferred for pumping H₂, a gas commonly used in semiconductorprocessing operations. It will be appreciated that other disk spacingsmay be preferred for pumping impurity gases other than H₂.

A preferred embodiment employing the above-described relationshipbetween getter element spacing and pumping speed is illustrated in FIG.8 at 800. There, the opposing faces of the adjacent getter elements arenot parallel with respect to each other, relative to the axes defined bythe apertures of elements 804, which apertures are aligned along an axisthat is parallel to heating element 210. As will be appreciated from theillustration, the axes of elements 204 are arranged such that thesurface planes 806 and 808 are not perpendicular to the axis defined bythe apertures. In a preferred embodiment, the apertures of the adjacentgetter elements are inclined along the axis at opposing angles, thusallowing adjacent getter elements to form a partial "V" shape.

FIG. 9 shows an alternative embodiment at 900 wherein adjacent getterelements 204 include hubs 304 having apertures that are substantiallyperpendicular to their common axis. In this embodiment, the faces of theadjacent getter elements are inclined relative to the axis formed bytheir apertures. In preferred embodiments, the opposing faces of thegetter elements, shown generally at 908 and 910, are inclined relativeto the axis and at opposing angles. Such an arrangement provides for asteady narrowing of the inter-element distance proceeding from theperipheral edges of the getter elements toward their hubs. Preferredangles and distances are described in Briesacher, et al., Ultra CleanTechnology 1(1):49-57 (1990), which is incorporated herein by reference.

Certain embodiments of the invention include straight and curved getterpump segments to accommodate the space restrictions inherent insemiconductor processing chambers. As shown in FIG. 10 at 1000, aprocessing chamber having a wall 103, heat lamps 1006 and 1008, and asputtering stage 106, includes a getter pump 1010 having getter elements204 supported on heating element 1014. The getter pump includes curvedportions 1018 and straight portions 1020 which allow placement of thegetter pump in close proximity to the sputter stage 106. It will beappreciated by those of skill in the art that maintaining closeproximity of the getter pump to the stage facilitates the pumping ofnon-noble gasses, and produces a low-impurity partial pressure wheresuch a partial pressure is most important-near the wafer beingprocessed.

It will be further appreciated by those skilled in the art that theplacement of the getters within an elongate, box-shaped shield structuresuch as shown in FIG. 2 can provide uneven exposure of the getterelements, with those portions of the getter elements closer to theaperture receiving greater exposure to the chamber atmosphere than thoseportions of the getter elements closer to the interior of the shields.Such an arrangement therefore could underutilize the sorptive capacityof the getter elements.

An embodiment of the getter segments of the present invention that wouldsubstantially avoid this potential problem is illustrated in FIG. 11 at1100. There, a shaft 1102 of a motor 1106 is coupled to a magneticcoupling device 1108 disposed on the outer side of a chamber wall 1105.A second magnetic coupling device 1110 is disposed on the other (inner)side of the chamber wall 1105. The magnetic coupling device 1110 iscoupled to the support/heater element 210 by a connector 1112.Optionally a heater element (not shown) external to the getter elementsmay be used with support/heater element 210.

In this alternate embodiment, getter pump module 1107 comprises aplurality of star-shaped getter assemblies 1114, which assemblies eachinclude a hub having a centrally located aperture and a plurality ofgetter elements 204a, 204b, 204c, 204d and 204e extending radially fromthe hub. The getter elements in this particular embodiment of theinvention are substantially paddle shaped, i.e., the getter elementshave a substantially rectangular or fan shaped cross section along anaxis which is longer than the width or depth of the getter element. Thegetter assemblies are supported by a heating element 210 which rotatesin the direction indicated.

Those skilled in the art will appreciate that such an embodiment willincrease the utilization of the capacity of the getter elements, asillustrated in FIG. 12 at 1200, where rotating getter pump 1202 isplaced inside shield 118. As the Figure illustrates, getter elements204a are in close proximity to the aperture of shield 118, therebyreceiving greater exposure to the chamber atmosphere relative to getterelements 204b which are in close proximity to the interior shield wall120. Rotation about central hub 1210 using motor 1212 allows the lesserexposed getter elements 204b to be moved forward toward the aperturewhile the more exposed getter elements 204a are moved toward the rear ofthe shield. Thus, the exposure across all of the getter elements is moreuniform.

Referring back to FIG. 2, it will be noted that in preferredembodiments, a thermally isolating shield is provided to isolatethermally the getter pump from the processing chamber. Such isolating isadvantageous as it protects the getter elements from the effects of theheat lamps that are used to "bake-off" residual gases from the surfacesof the walls and other components in the processing chamber, and,conversely, to protect the components in the chamber from heat releasedfrom the getter pump during regeneration of the getter elements.

Referring now to FIG. 13, a thermally shielded getter pump isillustrated at 1300. The shielded getter pump includes a box-likethermally isolating shield 118 shielding getter elements 204, whichgetter elements are supported by a support 124. The thermally isolatingshield preferably comprises an outer surface 1306 and a thermallyreflective inner surface 1308 which inner surface faces the getterelements 204. In preferred embodiments, the thermally isolating shieldincludes a floor shown generally at 1312 which catches various grains ofgetter material such as shown at 1310, which grains fall from the getterelements during normal operation. The thermally isolating shield willinclude an aperture such as shown at 1316 to allow contact between theatmosphere in the processing chamber and the getter elements. Theshields are preferably made from a stainless steel material, such as"316 Stainless Steel", and the interior surface of the shields may becoated or plated (such as with nickel) to enhance reflectivity.Alternatively, the shield may be polished or electropolished to enhancereflectivity, reduce porosity (which reduces gas and moistureadsorption), and minimize particulate contamination. Within central hub304 is disposed support/heater element 210. Optionally, an externalheater 134' can be used.

In some embodiments, the thermally isolating shield is an elongate,stationary box shaped structure which may be fixed to one or moresurfaces of the chamber interior. In some embodiments, the getterelements will be spaced relatively uniformly between the top, sides andbottom of the thermally isolating shield. Such an embodiment is commonlyreferred to as the aforementioned "low boy" structure. In otherembodiments, the spacing between the getter elements and the floor ofthe thermally isolating structure is larger than the spacing between thegetter elements and the remaining sides of the thermally isolatingshield. Such embodiments are typically referred to as the aforementioned"high boy" structure. These embodiments are denoted in FIG. 13 by theparameter "1". Preferably, 1 is about 0 mm for the "low boy"configuration and between about 13 mm and about 25 mm for the "high boy"configuration.

A second shield embodiment including a moveable shield is illustrated inFIGS. 14A and 14B. Such a moveable shield minimizes conductance loss byallowing substantially all of the getter elements to be exposed to thechamber atmosphere simultaneously, and yet can isolate the getterelements as desired for regeneration, system maintenance, duringbake-out, etc. As illustrated in FIG. 14A of 1400, a moveable shieldembodiment wherein the shield is in a closed position, i.e., all of theshield elements 1402, 1404 and 1406 are covering the getter elements, isdescribed. The shield elements rotate about hub 304 which hub issupported by support 124. The movable shield elements are, again,preferably made from stainless steel.

FIG. 14B illustrates an open position of the shield at 1420 in whichgetter element 204 is exposed substantially to the chamber atmosphere.The mechanism for opening and closing the shield is also illustrated. Ina preferred embodiment, the mechanism for opening and closing the shieldcomprises a flexible tube 1424 which tube includes a ring 1426 coupledto a one way valve 1428. The ring is further pivotably coupled to theproximal end of a rod 1429, which rod is slideably coupled to thegrooved extension of a gear 1430 which extension slideably receives thedistal end of the rod. The geared portion of gear 1430 is engaged with asmaller gear (not shown) which smaller gear is coupled to the shields1402, 1404 and 1406. When the tube is charged with gas and straightens,the rising of collar 1426 causes a rotation of gear 1430 which in turninitiates a larger rotation in the smaller gear thereby creating arotation of the shields about hub 1408 to a closed position. Conversely,when the tube is discharged and assumes its deflated position, thelowering of ring 1426 causes a rotation of the gears in the reversedirection, opening the shields. In this fashion, the shielded getterpump can be opened and closed remotely. However, it will be appreciatedthat various mechanical, electrical, hydraulic and/or pneumaticmechanisms can be adapted to achieve the same result.

Another view of the embodiment just described is illustrated in FIG. 15at 1500 which shows the shielded getter pump 1502 and the getterelements 204 and heating element 210 in a partial cut away at 1504. Theshield elements are shown at 1402 and 1406. A gas supply for operatingthe mechanism for opening and closing the shield is shown at 1512. Asecond, option al, gas supply (preferably nitrogen) for providing apositive pressure relative to the chamber's atmospheric pressure of agas is also shown at 1514. Preferably, the gasses supplied to the getterpump are inert gasses or nitrogen. In this fashion, the movable shieldcan be closed (by moving the shield elements in the direction of arrowA) and a nitrogen purge will isolate the getter elements from theambient environment. Nitrogen is also a preferred gas for providing a"passivating layer" over the getter element surfaces to protect thegetter elements from more harmful gasses, such as oxygen, as thenitrogen layer can be readily removed from the elements by heating(i.e., regeneration). This is particularly useful during systemmaintenance or repair where the chamber is open to the atmosphere, sinceprotecting the getter elements will enhance their useful life spans.

Thus, it will be see n that the present invention addressessubstantially the need to provide an apparatus and method for creatinghigh-vacuum conditions. Using the method and apparatus of the inventionas described herein, high-vacuum states, such as desired insemiconductor processing chambers, can be created more efficiently andeffectively than heretofore possible.

Although the invention has been described with reference to certainexamples and embodiments, it will be appreciated by those of skill inthe art that alternative embodiments can be made which do not departfrom the scope or spirit of the invention. It is therefore intended thatthe following appended claims be interpreted in light of the true spiritand scope of the present invention.

What is claimed:
 1. A getter pump comprising:a plurality of solid getterelements of porous, sintered getter material, each of said getterelements having an aperture extending therethrough; a metal rodextending through said apertures and supporting said getter elements;and a radiative heater for heating said getter elements and said metalrod, said radiative heater providing radiation which impinges on atleast some of said getter elements.
 2. A getter pump as recited in claim1, wherein said getter elements each further include a hub disposedwithin said aperture, wherein each of said hubs is provided with a hubaperture receptive to said metal rod.
 3. A getter pump as recited inclaim 2, wherein said hub aperture is cylindrical.
 4. A getter pump asrecited in claim 3, further comprising a spacer engaged with said metalrod and disposed between adjacent getter elements.
 5. A getter pump asrecited in claim 4, wherein said spacer is integral with said hub.
 6. Agetter pump as recited in claim 5, wherein said hub and spacer are madefrom a titanium-based material.
 7. A getter pump as recited in claim 2,wherein heat from said radiative heater in combination with heatconducted by said metal rod heats said getter elements to a regenerationtemperature.
 8. A getter pump comprising:a plurality of getter elements,each of said getter elements having an aperture extending therethrough;a metal rod extending through said apertures and supporting said getterelements; a means for radiantly heating said getter elements and saidmetal rod, said heating means providing radiation which impinges on atleast some of said getter elements; and a thermally isolating shieldproximate to said getter elements and at least partially surroundingsaid getter elements.
 9. A getter pump as recited in claim 8, whereinsaid means for radiantly heating said getter elements and said metal rodcomprises an infrared lamp.
 10. A getter pump as recited in claim 8,wherein said getter elements are substantially disk-shaped members. 11.A getter pump as recited in claim 10, wherein said getter elements areporous, sintered disks of getter material each having a centrallylocated hub of non-getter material.
 12. A getter pump as recited inclaim 8, wherein said shield is a fixed shield.
 13. A getter pump asrecited in claim 12, wherein said fixed shield comprises a reflectivesurface which faces said getter elements.
 14. A getter pump as recitedin claim 13, wherein said fixed shield is an elongated box-shaped shieldhaving at least one open side.
 15. A getter pump as recited in claim 12,wherein said fixed shield causes no more than a 25% conductance lossbetween said getter elements and an environment surrounding said fixedshield.
 16. A getter pump comprising:a getter assembly including a hubhaving a centrally located aperture, and a plurality of getter elementsextending substantially radially from said hub; a metal rod extendingthrough said aperture of said hub to support said getter elements; and aradiative heater for heating said getter elements and said metal rod,said radiative heater providing radiation which impinges on at leastsome of said getter elements.
 17. A getter pump as recited in claim 16,wherein said getter assembly is one of a plurality of getter assembliessupported by said metal rod.
 18. A getter pump as recited in claim 17,further including a thermally isolating shield surrounding at leastpartially said getter elements and said radiative heater.
 19. A getterpump as recited in claim 18, wherein said shield in an elongatedbox-shaped shield.
 20. A getter pump, comprising a plurality of solidporous getter elements of porous, sintered getter material, each of saidgetter elements having an aperture therethrough, a metal rod extendingthrough said apertures and supporting said getter elements, and aradiative heater for heating said getter elements and said metal rod,said radiative heater providing radiation which impinges on at leastsome of said getter elements, said getter elements and said radiativeheater being at least partially enclosed within a thermally isolatingshield, said shield having walls proximate to said getter elements andsaid radiative heater, wherein said getter pump has at least about a 75%conductance with a proximate volume to be pumped.
 21. A getter pump asrecited in claim 20, wherein said heater is a resistive heater.
 22. Agetter pump comprising a plurality of getter elements having a commonsupport structure, said suppport structure comprising a metal rod whichextends through an aperture in each of said getter elements, each ofsaid getter elements comprising a solid getter body of porous, sinteredgetter material, and a radiative heater for heating said getter elementsand said support structure, said radiative heater providing radiationwhich impinges on at least some of said getter elements, wherein saidsupport structure is coupled with a thermally isolating shield.
 23. Thegetter pump of claim 22, wherein said radiative heater is an infraredlamp.
 24. The getter pump of claim 23, wherein each of said getterelements further comprises a hub engaged with said getter element, eachsaid hub being provided with an aperture.